Three-component metal hydride-transition metal halide catalyst and olefin polymerization process therewith



United States THREE-COMPONENT METAL HY BRIDE-TRANSI- TION METAL HALIDE CATALYST AND OLEFIN POLYMERIZATION PROCESS THEREWITH Harry W. Coover, Jr. and Frederick B. Joyner, Kingsport, Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey This invention relates to a new and improved polymerization process and is particularly concerned with the use of a novel catalyst combination for preparing high molecular weight solid polyolefins, such as polypropylene, of high density and crystallinity. In a particular aspect the invention is concerned with the preparation of polypropylene and higher polyolefins having a high density using a particular catalyst combination which has unexpected catalytic activity and which gives products characterized by unusually high crystallinity, softening point, thermal stability, stiffness and being substantially free of non-crystalline polymers.

Polyethylene has heretofore been prepared by high pressure processes to give relatively flexible polymers having a rather high degree of chain branching and a density considerably lower than the theoretical density. Thus, pressures of the order of 500 atmospheres or more and usually of the order of 1000-1500 atmospheres are commonly employed. It has been found that more dense polyethylenes can be produced by certain catalyst combinations to give polymers which have very little chain branching and a high degree of crystallinity. The exact reason why certain catalyst combinations give these highly dense and highly crystalline polymers is not readily understood. Furthermore, the activity of the catalysts ordinarily depends upon certain specific catalyst combinations, and the results are ordinarily highly unpredictable, since relatively minor changes in the catalyst combination often lead to liquid polymers rather than the desired solid polymers.

Some of the catalysts that the effective for producing crystalline high density polyethylene cannot be used to produce a similar type of polypropylene. For example, catalyst combinations of metal hydrides with transition element compounds have been suggested for ethylene polymerization, but these catalysts are relatively ineffective for polymerizing propylene to form high density crystalline polymers. Thus, one cannot predict whether a specific catalyst combination will be effective to produce crystalline high density polymers with specific tat-olefins.

This invention is concerned with and has for an object the provision of improved processes whereby u-monoolefins and particularly propylene can be readily polymerized by catalytic means to give high molecular weight, highly crystalline polymers. A particular object of the invention is to provide an improved catalyst combination which has unexpected catalytic activity for the polymerization of a-monoolefins to form crystalline high density polymers. Other objects will be apparent from the description and claims which follow.

The above and other objects are attained by means of this invention, wherein a-monoolefins, either singly or in admixture, are readily polymerized to high molecular weight solid polymers by efiecting the polymerization in the presence of a catalytic mixture containing a hydride of a group IA or group IIA metal, a halide of a transition metal selected from the group consisting of titanium,

tent

Patented Jan. 10, 1961 zirconium, vanadium, chromium and molybdenum, the halogen atoms being chlorine, bromine or iodine, and a third component selected from the compounds having the formulas:

wherein each Y is an alkylamino (-NR or alkoxy (-OR), said R being an alkyl radical containing 1 to 8, preferably 1 to 4 carbon atoms and wherein n is an integer of 1 to 4. The catalytic activity of this mixture was wholly unexpected, particularly since metal hydrides either singly or in admixture with transition element halides had not been known to possess catalytic activity for forming crystalline polymers of propylene and higher olefins, and the third component of the catalyst is not a polymerization catalyst. The inventive process is carried out in liquid phase in an inert organic liquid and preferably an inert liquid hydrocarbon vehicle. The process proceeds with excellent results over a temperature range of from 0 C. to 250 C. although it is preferred to operate within the range of from about 50 C. to about 150 C. Likewise, the reaction pressures may be varied widely from about atmospheric pressure to very high pressures of the order of 20,000 p.s.i. or higher. A particular advantage of the invention is that pressures of the order of 30-1000 p.s.i. give excellent results, and it is not necessary to employ the extremely high pressures which were necessary heretofore. The liquid vehicle employed is desirably one which serves an inert liquid reaction medium.

The invention is of particular importance in the preparation of highly crystalline polypropylene, the polybutenes and polystyrene, although it can be used for polymerizing ethylene, mixtures of ethylene and propylene as well as other ot-monoolefins containing up to 10 carbon atoms. The polyethylene which is obtained in accordance with this invention has a softening or fusion point greater than 120 C. whereby the products prepared therefrom can be readily employed in contact with boiling water without deformation or other deleterious effects. The process of the invention readily results in solid polymers having molecular weights greater than 1000 and usually greater than 10,000. Furthermore, polymers having molecular weights of as much as 1,000,000 or higher can be readily prepared if desired. The high molecular weight, high density polyethylenes of this invention are insoluble in solvents at ordinary temperatures but they are soluble in such solvents as xylene, toluene or tetralin at temperatures above 100 C. These solubility characteristics make it possible to carry out the polymerization process under conditions wherein the polymer formed is soluble in the reaction medium during the polymerization and can be precipitated therefrom by lowering the temperature of the resulting mixture.

The polyethylenes of this invention are highly crystalline and usually exhibit crystallinity above as shown by X-ray diagrams. Ordinarily, the crystallinities of the polyethylenes obtained by this process average close to In contrast to the high pressure polyethylene known heretofore, the number of methyl groups per hundred carbon atoms in the polyethylenes of this invention are of the order of 0.5 or lower. The densities are of the order of 0.945 or higher, with densities of the order of 0.96 or higher being obtained in many cases. inherent viscosity as measured in tetralin at 145 C. can be varied from about 0.5 or lower to 5.0 or higher. Melt indices as measured by the standard ASTM method may be varied from about 0.1 to or even higher.

The novel catalysts described above are particularly useful for polymerizing propylene to form a crystalline, high-density polymer.

The

The polypropylene produced has a softening point above 155 C. and a density of 0.91 and higher. Usually the density of the polypropylene is of the order of 0.91 to 0.92.

The polyolefins prepared in accordance with the invention can be molded or extruded and can be used to form plates, sheets, films, or a variety of molded objects which exhibit a higher degree of stiifness than do the corresponding high pressure polyolefins. The products can be extruded in the form of pipe or tubing of excellent rigidity and can be injection molded into a great variety of articles. The polymers can also be cold drawn into ribbons, bands, fibers or filaments of high elasticity and rigidity. Fibers of high strength can be spun from the molten polyolefins obtained according to this process.

As has been indicated above the improved results obtained in accordance with this invention depend upon the particular catalyst combination. Thus, one of the components of the catalyst is a hydride of a metal from groups IA and IIA. Specifically, hydrides containing the above metals and another metal such as aluminum, for example, sodium aluminum hydride, lithium aluminum hydride, and the like can be used in the catalyst compositions. Another component of the catalyst composition is a halide of a transition metal selected from the group consisting of titanium, zirconium, vanadium, chromium and molybdenum. In these compounds the transition metal is preferably at its maximum valence, but a compound of a transition metal having a reduced valance can be used. Also, the halogen is selected from the group consisting of chlorine, bromine and iodine. Such compounds as titanium tetrachloride, titanium trichloride, titanium dichloride, titanium tetrabromide, titanium tetraiodide, titanium tribromide and titanium triiodide can be used in the catalyst composition. Similar halides of zirconium, vanadium, chromium and molybdenum can also be used. For the most desirable results it is preferred to use a halide of titanium having either its maximum valency or a reduced valency and specifically it is preferred to employ either titanium tetrachloride or titanium trichloride in the catalyst composition. The third component of the catalyst composition is a compound having the formula:

Each Y represents a lower alkylamino or lower alkoxy radical, R is a lower alkyl radical containing 1 to 8 preferably 1 to 4, carbon atoms and n is an integer of 1 to 4.

Among the specific compounds that can be used are tris-N,N-dimethyl phosphoramide, triethyl phosphate, mixed phosphate ester-amides, triethyl phosphite, N,N- dimethylacetamide, adipamide and the like. The catalyst compositions of this invention when reacted with water do not produce hydrogen.

The limiting factor in the temperature of the process appears to be the decomposition temperature of the catalyst. Ordinarily temperatures from 50 C. to 150 C. are employed, although temperatures as low as C. or as high as 250 C. can be employed if desired. Usually, it is not desirable or economical to effect the polymerization at temperatures below 0 C., and the process can be readily controlled at room temperature or higher which is an advantage from the standpoint of commercial processing. The pressure employed is usually only sufiicient to maintain the reaction mixture in liquid form during the polymerization, although higher pressures can be used if desired. The pressure is ordinarily achieved by pressuring the system with the monomer whereby additional monomer dissolves in the reaction vehicle as the polymerization progresses.

The polymerization embodying the invention can be carried out batchwise or in a continuous flowing stream process. The continuous processes are preferred for economic reasons, and particularly good results are obtained using continuous processes wherein a polymerization mixture of constant composition is continuously and progressively introduced into the polymerization zone and the mixture resulting from the polymerization is continuously and progressively withdrawn from the polymerization zone at an equivalent rate, whereby the relative concentration of the various components in the polymerization zone remains substantially unchanged during the process. This results in formation of polymers of extremely uniform molecular weight distribution over a relatively narrow range. Such uniform polymers possess distinct advantages since they do not contain any substantial amount of the low molecular weight or high molecular weight formations which are ordinarily found in polymers prepared by batch reactions.

In the continuous flowing stream process, the temperature is desirably maintained at a substantially constant value within the preferred range in order to achieve the highest degree of uniformity. Since it is desirable to employ a solution of the monomer of relatively high concentration, the process is desirably effected under a pressure of from 30 to 1000 p.s.i. obtained by pressuring the system with the monomer being polymerized. The amount of vehicle employed can be varied over rather wide limits with relation to the monomer and catalyst mixture. Best results are obtained using a concentration of catalyst of from about 0.1% to about 2% by weight based on the weight of the vehicle. The concentration of the monomer in the vehicle will vary rather widely depending upon the reaction conditions and will usually range from about 2 to 50% by weight. For a solution type of process it is preferred to use a concentration from about 2 to about 10% by weight based on the weight of the vehicle, and for a slurry type of process higher concentrations, for example, up to 40% and higher are preferred. Higher concentrations of monomer ordinarily increase the rate of polymerization, but concentrations above 510% by weight in a solution process are ordinarily less desirable because the polymer dissolved in the reaction medium results in a very viscous solution.

The molar ratio of hydride to transition metal halide can be varied within the range of 1:0.5 to 1:2, and the molar ratio of hydride to the third component of the catalytic mixture can be varied within the range of 1:1 to 1:025, but it will be understood that higher and lower molar ratios are within the scope of invention. The polymerization time can be varied as desired and will usually be of the order of from 30 minutes to several hours in batch processes. Contact times of from 1 to 4 hours are commonly employed in autoclave type reactions. When a continuous process is employed, the contact time in the polymerization zone can also be regulated as desired, and in some cases it is not necessary to employ reaction or contact times much beyond one-half to one hour since a cyclic system can be employed by precipitation of the polymer and return of the vehicle and unused catalyst to the charging zone wherein the catalyst can be replenished and additional monomer introduced.

The organic vehicle employed can be an aliphatic alkane or cycloalkane such as pentane, hexane, heptane or cyclohexane, or a hydrogenated aromatic compound such as tetrahydronaphthalene or decahydronaphthalene, or a high molecular weight liquid paraffin or mixture of pan aflins which are liquid at the reaction temperature, or an aromatic hydrocarbon such as benzene, toluene, xylene, or the like, or a halogenated aromatic compound such as chlorobenzene, chloronaphthalene, or orthodichlorobenzene. The nature of the vehicle is subject to considerable variation, although the vehicle employed should be liquid under the conditions of reaction and relatively inert. The hydrocarbon liquids are desirably employed. Other solvents which can be used include ethyl benzene,

isopropyl benzene, ethyl toluene, n-propyl benzene, di-v gnomes ethyl benzenes, mono and dialkyl naphthalenes, n-octane, isooctane, methyl cyclohexane, tetralin, decalin, and any of the other well-known inert liquid hydrocarbons. The diluents employed in practicing this invention can be advantageously purified prior to use in the polymerization reaction by contacting the diluent, for example, in a distillation procedure or otherwise, with the polymerization catalyst to remove undesirable trace impurities. Also, prior to such purification of the diluent the catalyst can be contacted advantageously with polymerizable amonoolefin.

The polymerization ordinarily is accomplished by merely admixing the components of the polymerization mixture, and no additional heat is necessary unless it is desired to effect the polymerization at an elevated temperature in order to increase the solubility of polymeric product in the vehicle. When the highly uniform polymers are desired employing the continuous process wherein the relative proportions of the various components are maintained substantially constant, the temperature is desirably controlled within a relatively narrow range. Th1s 1s readily accomplished since the solvent vehicle forms a high percentage of the polymerization mixture and hence can be heated or cooled to maintain the temperature as desired.

A particularly effective catalyst for polymerizing ethylene, propylene, styrene and other u-monoolefins in accordance with this invention is a mixture of lithium aluminum hydride, titanium tetrachloride and tris-N,N- dimethyl phosphoramide. The importance of the various components of this reaction mixture is evident from the fact that a mixture of the hydride and chloride is relatively ineflective for polymerizing propylene to crysatlline polymer and large amounts of oils and rubbers are produced in a propylene polymerization. However, when the above phosphoramide or other third compound within the scope of this invention is added to the mixture the resulting catalyst composition is highly effective for polymerizing propylene to form a highly crystalline highdensity, high softening polymer without the formation of oils and rubbers.

Thus, by means of this invention polyolefins such as polyethylene and polypropylene are readily produced using a catalyst combination which, based on the knowledge of the art, would not be expected to be effective. The polymers thus obtained can be extruded, mechanically milled, cast or molded as desired. The polymers can be used as blending agents with the relatively more flexible high pressure polyethylenes to give any desired combination of properties. The polymers can also be blended with antioxidants, stabilizers, plasticizers, fillers, pigments, and the like, or mixed with other polymeric materials, waxes and the like. In general, aside from the relatively higher values for such properties as softening point, density, stiffness and the like, the polymers embodying this invention can be treated in similar manner to those obtained by other processes.

From the detailed disclosure of this invention it is quite apparent that in this polymerizaiton procedure a novel catalyst, not suggested in prior art polymerization procedures, is employed. As a result of the use of this novel catalyst it is possible to produce polymeric hydrocarbons, particularly polypropylene, having properties not heretofore obtainable. For example, polypropylene prepared in the presence of catalyst combinations within the scope of this invention is substantially free of rubbery and oily polymers and thus it is not necessary to subject such polypropylene of this invention to extraction procedures in order to obtain a commercial product. Also polypropylene produced in accordance with this invention possessesunexpectedly high crystallinity, an unusually high of softening point and outstand ing thermal stability. Suc'h polypropylene also has a very high stiffness as a result of the unexpectedly high crystallinity. The properties imparted to polypropylene 6 prepared in accordance with this invention thus charac terize and distinguish this polypropylene from polymers prepared by prior art polymerization procedures.

The novel catalysts defined above can be used to produce high molecular weight crystalline polymeric hydrocarbons. The molecular weight of the polymers can be varied over a wide range by introducing hydrogen to the polymerization reaction. Such hydrogen can be introduced separately or in admixture with the olefin monomer. The polymers produced in accordance with this invention can be separated from polymerization catalyst by suitable extraction procedures, for example, by washing with water or lower aliphatic alcohols such as methanol.

The catalyst compositions have been described above as being effective primarily for the polymerization of tic-monoolefins. These catalyst compositions can, how'- ever, be used for polymerizing other a-olefins, and it is not necessary to limit the process of the invention to monoolefins. Other u-olefins that can be used are butadiene, isoprene, 1,3-pentadiene and the like.

The following examples are illustrative of this invention.

Example I This example illustrates the relatively large quantity of rubbery polymer obtained with a two-component alkali metal hydride-transition metal compound catalyst. In a nitrogen-filled dry box a l-g. catalyst charge comprising equimolar quantities of sodium hydride and titanium tetrachloride was added to a 500-ml. pressure bottle along with ml. of dry heptane. The pressure bottle was then capped, removed from the dry box, and attached to a propylene source provided by means of a converted Parr hydrogenation apparatus. The mixture was agitated, heated to 85 C., and maintained under 30 p.s.i. propylene pressure for 6 hours. At the end of this period the resulting polymer was washed several times with dry methyl alcohol and then with water. The weight of the polypropylene was 12.5 g. having a density of 0.898 and an inherent viscosity of 1.99. After extraction of the rubbery polypropylene by the use of butyl ether a 70 C., residual highly crystalline polypropylene weighed 4.2 g., had a density of 0.917, and an inherent viscosity at C. in tetralin of 2.22.

When TiCl replaced TiCl under the above conditions, a slight increase in crystallinity of the product was noted. The 9.5 g. of polypropylene had a density of 0.903 and an inherent viscosity of 2.10. After extraction with butyl ether, the polypropylene weighed 7.6 an inherent viscosity of 2.45.

residual highly crystalline Example 2 This example illustrates the relatively large quantityof rubbery polymer obtained With a two-component mixed hydride catalyst. l-gram catalyst charge comprising equimolar quantities of lithium aluminum hydride and titanium tetrachloride. was added to a 500-ml. pressure bottle along with '100 ml. of dry heptane. The pressure bottle was then capped, removed from the dry box, and attached to a propylene source provided by means of a converted Parr hydrogenation apparatus. The mixture was agitated,

g. and had a 0.915 density and In a nitrogen-filled dry box a heated to 55 C., and maintained under 30 p.s.i. propylene pressure for 6 hours. At the end of this period, the resulting polymer was washed several times with dry methanol and then with water. The Weight of the polypropylene was 21.0 g. having a density of 0.894 and an inherent viscosity of 1.13. After extraction of the rubbery polypropylene by the use of butyl ether at 70 C., the residual highly crystalline polypropylene weighed 4.3 g., had a density of 0.917 and an inherent viscosity of 1.75.

When calcium hydride was used in place of the lithium aluminum hydride in the above example, the yield of polypropylene was 18.3 g. having a density of 0.898 and an inherent viscosity of 1.70. After extraction with butyl ether, the residual highly crystalline polypropylene weighed 6.0 g. and had a 0.918 density and an inherent viscosity of 2.15.

Example 4 When the process of Example 3 was repeated using a l-g. catalyst charge having a 1:1:0.5 molar ratio of lithium aluminum hydride, titanium tetrachloride, and tris-N,N-dimethyl phosphoramide, the yield of crystalline polypropylene was 23.7 g. with a density of 0.919 and an inherent viscosity of 2.60. Equally good results were obtained by using triethyl phosphite or N,N-dimethylacetamide in place of the phosphoramide.

Example In a nitrogen-filled dry box, a dry 280-ml. stainless steel autoclave was loaded with a 2-gram catalyst charge comprising a 2:1:0.1 molar ratio of calcium hydride, titanium trichloride, and tris N,N dimethyl phosphoramide. The autoclave was capped, removed from the dry box, placed in a rocker, and attached to a propylene source. A IOO-ml. (51 grams) charge of propylene was added, the autoclave was rocked, heated to 150 C. and maintained there for four hours. The product was isolated by washing with dry methanol and then with water. A 35.0 gram yield of highly crystalline polypropylene was obtained having a density of 0.92 and an inherent viscosity of 3.44.

The above run was repeated using triethyl phosphate, triethyl phosphite, N,N-dimethylacetamide and adiparnide in place of the tris-N,N-dimethyl phosphoramide in the above catalyst.

Example 6 The process of Example 5 was used with 0.75 grams.

of a catalyst having a 1:1:0.25 molar ratio of potassium hydride, titanium trichloride, and tris-N,N-dimethyl phosphoramide. A 38.3-gram yield of polypropylene was obtained having a density of 0.92 and an inherent viscosity of 3.14.

When titanium trichloride in the above catalyst is replaced by zirconium tetrachloride, chromic chloride, or molybdenum pentachloride improved yields of polypropylene are realized. Similarly, highly crystalline polyolefins were also obtained by using 3-methyl-1-butene, 4 methyl-l-pentene, l-butene, 1-pentene, styrene, fluorostyrene and vinyl cyclohexane as monomers in place of propylene.

We claim:

1. In the polymerization of a-monoolefinic hydrocarbons containing 3 to 8 carbon atoms to form solid crystalline polymer, the improvement which comprises catalyzing the polymerization reaction with a catalytic mixture consisting essentially of a hydride selected from the group consisting of sodium hydride, potassium hydride, calcium hydride and lithium aluminum hydride, a chloride of a transition metal selected from the group consisting of titanium, zirconium, vanadium, chromium and molybdenum and an organophosphorus compound selected from the group consisting of tri-lower alkyl phosphites, trilower alkyl phosphates and hexalower alkyl phosphoric triamides, the molar ratio of hydride to organophosphorus compound being within the range of 1:1 to 120.25.

2. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of sodium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 1:025.

3. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises efiecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of potassium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 110.25.

4. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of calcium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 1:025.

5. In the polymerization of propylene to form solid crystalline polymer, the improvement which comprises effecting the polymerization in liquid dispersion in an inert hydrocarbon liquid and in the presence of a catalytic mixture consisting essentially of lithium aluminum hydride, titanium tetrachloride, and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 120.25.

6. As a composition of matter, a polymerization catalyst consisting essentially of a hydride selected from the group consisting of sodium hydride, potassium hydride, calcium hydride and lithium aluminum hydride, a chloride of a transition metal selected from the group consisting of titanium, zirconium, vanadium, chromium and molybdenum and an organophosphorus compound selected from the group consisting of tri-lower alkyl phosphites, tri-lower alkyl phosphates and hexa-lower alkyl phosphoric triamides, the molar ratio of hydride to organophosphorus compound being Within the range of 1:1 to 120.25.

7. As a composition of matter, a polymerization catalyst consisting essentially of sodium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 1:025.

8. As a composition of matter, a polymerization catalyst consisting essentially of potassium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 120.25.

9. .As a composition of matter, a polymerization catalyst consisting essentially of calcium hydride, titanium trichloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 1:025.

10. As a composition of matter, a polymerization catalyst consisting essentially of lithium aluminum hydride, titanium tetrachloride and tris-N,N-dimethyl phosphoramide, the molar ratio of hydride to phosphoramide being within the range of 1:1 to 1:025.

References Cited in the file of this patent UNITED STATES PATENTS 2,839,474 Johnson et al. June 18, 1958 2,840,617 Shokal June 24, 1958 2,846,427 Findlay Aug. 5, 1958 2,862,917 Anderson et al. Dec. 2, 1958 2,874,153 Bowman Feb. 17, 1959 

1. IN THE POLYMERIZATION OF A-MONOOLEFINIC HYDROCARBONS CONTAINING 3 TO 8 CARBON ATOMS TO FORM SOLID CRYSTALLINE POLYMER, THE IMPROVEMENT WHICH COMPRISES CATALYZING THE POLYMERIZATION REACTION WITH A CATALYIC MIXTURE CONSISTING ESSENTIALLY OF A HYDRIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM HYDRIDE, POTASSIUM HYDRIDE, CALCIUM HYDRIDE AND LITHIUM ALUMINUM HYDRIDE, A CHLORIDE OF A TRANSITION METAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM, ZIRCONIUM, VANADIUM, CHROMIUM AND MOLYBDENUM AND AN ORGANOPHOSPHORUS COMPOUND SELECTED FROM THE GROUP CONSISTING OF TRI-LOWER ALKYL PHOSPHITES, TRILOWER ALKYL PHOSPHATES AND HEXALOWER ALKYL PHOSPHORIC TRIAMIDES, THE MOLAR RATIO OF HYDRIDE TO ORGANOPHOSPHORUS COMPOUND BEING WITHIN THE RANGE OF 1:1 TO 1:0.25. 